NEO-M9N - Integration manual
is 9 bytes and the maximum 24 bytes, the typical size is 10 or 11 bytes. If the odometer is enabled
then this will use at least another three bytes per fix.
Each log also has a fixed overhead which is dependent on the log type. The approximate size of this
overhead is shown in the following table.
Log type
Overhead
circular
Up to 40 kB
non-circular
Up to 8 kB
Table 10: Log overhead size
The number of entries that can be logged in any given flash size can be estimated as follows:
Approx. number of entries = (flash size available for logging - log overhead)/typical entry size
For example, if 1500 kB of flash is available for logging (after other flash usage such as the firmware
image is taken into account) a non-circular log would be able to contain approximately 139000
entries: ((1500*1024)- (8*1024))/11 = 138891.
3.4.4 Recording
The CFG-LOGFILTER-RECORD_ENA configuration item must be set to
true
to enable recording into
the log. Nothing will be recorded if recording is disabled, otherwise position fix and UBX-LOG_STRING
entries can be recorded. When recording is enabled an entry will also be created from each UBX-LOG-
STRING message. These will be timestamped if the receiver has current knowledge of time.
The CFG-LOGFILTER-* configuration group has several values which can be used to select position
fix entries for logging. If CFG-LOGFILTER-APPLY_ALL_FILTERS is
false
, then all position fixes will
be logged (subject to a maximum rate of 1 Hz). Otherwise, a position is logged if any of the or if
all of MIN_INTERVAL, TIME_THRS, SPEED_THRS or POSITION_THRS thresholds are exceeded. If a
threshold is set to zero it is ignored.
Position fixes are only recorded if a valid fix is obtained. Failed and invalid fixes are not recorded.
Position fixes are compressed to reduce the amount of flash space used. In order to improve the
compression, the fix values are rounded. This means that the values returned by the logging system
may differ slightly from those that are gathered in real time.
The recorded data for a fix comprises:
• The time and date of the fix recorded to a precision of one second.
• Latitude and longitude to a precision of one millionth of a degree. Depending on position on Earth
this is a precision in the order of 0.1 m.
• Altitude (height above mean sea level) to a precision of 0.1 m. Entries with an altitude lower than
-470 m (lower than the lowest point on earth) or higher than 20,000 m may not be recorded in
the log.
• Ground speed to a precision of 1 cm/s.
• The fix type (only successful fix types, since these are the only ones recorded).
• The number of satellites used in the fix is recorded, but there is a maximum count which can
be recorded. If the actual count exceeds this maximum count then the maximum count will be
recorded. If a log entry is retrieved with a satellite count equal to the maximum this means that
value or more. The maximum count is 51.
• A horizontal accuracy estimate is recorded to give an indication of fix quality. This is an
approximate compressed representation of the accuracy as determined by the fix process. Any
accuracy less than 0.7 m will be recorded as 0.7 m and any value above 1 km will be recorded
UBX-19014286 - R07
3 Receiver functionality
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